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相干调制是近年来水声通信领域中最为活跃的研究课题之一。但水声信道的时变多途效应造成接收数据严重的码间干扰（ Ｉ Ｓ Ｉ），使得高速水声通讯的实现十分困难。盲符号估计不需要利用已知序列对滤波器参数进行周期训练，从而能有效地节省信道带宽。利用盲估计方法克服 Ｉ Ｓ Ｉ的关键在于，对多途接收的有噪信号进行多倍码速率的采样，将信道等效为一个单输入多输出系统，并构造采样输出的循环平稳序列的二阶统计量，去估计原发送序列。本文针对水声信道的实际特点，提出了一种盲符号估计的新方法。与文献［３］的算法相比，它具有更低的运算量，便于数据的实时处理。文中最后利用计算机仿真结果验证了该算法的有效性。
Coherent modulation is one of the most active research topics in underwater acoustic communication in recent years. However, the time-varying multi-path effects of underwater acoustic channels cause serious inter-symbol interference (I S I) of received data, which makes the realization of high-speed underwater acoustic communication very difficult. The blind symbol estimation does not need periodic training of the filter parameters by using the known sequence, so that the channel bandwidth can be effectively saved. The key to overcoming I S I by using blind estimation method is to sample the multi-times code rate of the noisy signal received from multiple paths, to make the channel equivalent to a single-input multiple-output system and to construct the second Order statistics, to estimate the original sending sequence. In this paper, aiming at the actual characteristics of underwater acoustic channel, a new method of blind symbol estimation is proposed. Compared with the algorithm of [3], it has a lower computational complexity and facilitates the real-time processing of data. Finally, the computer simulation results verify the effectiveness of the algorithm.